How do some apps get away with Ads on 3rd party content? (ie Reddit Apps)

From what I have read, most app stores and ad networks don't let you use someone else's content in your app and then show ads.

How are apps such as all the Reddit apps doing this? For example I am using "Now for Reddit" on Android and there are banner ads all over. This is not developed by reddit, so what is the deal?

Thanks

Well in case anyone was interested, i found the answer myself from the app dev:

"We've had issues ourselves before and have had to provide advertising companies with our reddit licence agreement to ensure we stay the right side of the rules."